During the process of petroleum drilling, once the reservoir damage occurs, permeability of the reservoir is reduced, and flow resistance of oil gas is increased, so that the capacity of the oil gas well is reduced and accuracy of well testing and well logging interpretation is influenced, which may cause misinterpretation and missing of reservoir, thereby causing great economic damages, which are serious consequences. Therefore, it is crucial to protect the reservoir during the process of drilling well.
During the process of drilling well, the drilling fluid can easily invade the pore of the reservoir, through particle jam and (or) water-sensitive functions and the like, causing a reduction in reservoir permeability, and damaging the reservoir. During the process of drilling a well, adding a reservoir protecting agent into the drilling fluid is a commonly adopted method for protecting the reservoir. The conventional reservoir protecting agent is calcium carbonate.
The calcium carbonate is generally in the form of rigid particles, and after entering into the pore of the reservoir under the action of the pressure difference, follows the process of “selectively bridging, and filling step-by-step.” The bridging function of calcium carbonate particles with larger size, the bridging and filling functions of calcium carbonate particles with smaller size, and the filling function of deformable particles (such as pitch) are required (see FIG. 1). A blocking layer with a permeability of almost zero is formed inside the void, which stops the drilling fluid from continuously invading the reservoir, thereby achieving the function of protecting the reservoir.
However, as a reservoir protecting agent, calcium carbonate has the following problems: (1) the calcium carbonate relates to rigid particles, the blocking effect is not ideal when using separately, and it is necessarily used with deformable particles such as the types of pitch; (2) the calcium carbonate enters into inside the pore of the reservoir for blocking, which requires strictly matching the diameter of the particle with the diameter of the pore of the reservoir, or the blocking effect is not good; and (3) the calcium carbonate enters into the pore of the reservoir for blocking, acidification and eliminating plugging are necessarily performed after the well is drilled, so that the blocking can be removed, the reservoir permeability is recovered, and the oil gas well can functionally produce.